The present invention relates to sealing device arrange to provide the seal for a fluid, in particular a liquid, between any ambient and the inside of a cavity situated between a stationary member and a rotatable member.
The sealing device according to the invention is of the axial type, i.e. it is arranged to prevent foreign matters from entering un annular space between two surfaces, one of the rotatable member and the other of stationary member, substantially orthogonal to the axis of rotation of the first mentioned member.
Sealing devices of this type are widely used in machines of various types, for example to avoid penetration of materials, in particular fluids, into the cavity which surrounds the surface of a rotating shaft. Such devices are utilized in the rotating drilling tools intended to carry out drilling operations in the mining or oil fields; a tool of this type comprises substantially some rotatable toothed discs each of which is supported by means of rolling and/or plsin bearings on a corresponding pin protruding from a support bar. To avoid penetration of foreign matters (mud, drilling mud, dust) into the cavity of such discs, in which the bearings are located, sealing devices of the mentioned type are provided between the disc and the support bar.
Such sealing devices comprise normally a metal ring coated usually by means of rubber having such a cross-section (for example an S-shaped cross-section) as to be deformable axially, which ring is disposed between two surfaces, one of the stationary member and the other of the rotatable member, orthogonal to the axis of rotation of the latter. Because of the resilient deformation produced by mounting a ring of the type mentioned above between the said surfaces, high axial pressures are exerted between the coupled surfaces of the said ring and the said two members, which pressures are capable of preventing the penetration of foreign matters between those surfaces.
However, the sealing devices of this type have the disadvantage consisting in that they cannot be utilized in the cases in which the pressure of the fluid for which the seal has to be provided is particularly high; in fact, in such cases, the resultant of such pressure is in a position to deform the said sealing ring, thus irremediably damaging it and/or considerably increasing the value of the pressure exchanged between the ring and the coupled surfaces of stationary and rotating members, thus giving rise to severe wear and to seizures.
To avoid the above disadvantages, pressure balancing means are sometimes utilized in association with the devices of the type mentioned hereinabove, which balancing means are arranged to increase the pressure inside the cavity as the outside pressure increases. The sealing devices provided with pressure balancing means obviously result in being complex, rather delicate and bulky.